This invention relates to catheter designs and methods of positioning and making catheter designs. More particularly, the invention relates to catheter designs that increase flow through a catheter as well as methods for positioning a catheter of these designs and making a catheter of these designs.
Dialysis procedures, for example, frequently use dual lumen catheters to transport blood from a patient to a dialysis machine and then return processed blood back to the patient. See, e.g., McIntosh et al., JAMA 169(8): 137-38 (1959). Functionality, comfort, ease of manufacture, and ease of use are all important considerations for catheter designs. Specifically, high flow rates through catheters are necessary to maximize the efficiency of dialysis procedures. Both the physiology of blood and the designs of conventional catheters limit flow rate. Blood cells cannot survive high pressure differentials or excessive mechanical shear.
Conventional catheters have a design which, while useful, does not maximize flow rate within the bounds of these physiological constraints. Additionally, conventional catheter designs have several other disadvantages. First, an intake lumen positioned with a vessel often becomes suctioned against the vessel wall, reducing flow through the catheter. Second, a shaft of a conventional catheter is prone to kinking, again reducing flow. Third, an internal septum that divides multiple lumens within a catheter is prone to deflection due to pump pressure.
It has been discovered that one can maximize the flow rate though a catheter despite design constraints of maximal catheter outer diameter (xe2x80x9cfrench sizexe2x80x9d) and bounded allowable pressure drop. In catheter designs of the present invention, one can tailor a catheter""s internal geometry, the thickness of a catheter""s wall and internal divider, and/or the ability of a catheter""s internal divider to resist flexure when exposed to a pressure gradient in order to reduce resistance to flow, reduce the catheter""s tendency to kink, and maximize flow rate. These design concepts are applicable equally to single lumen catheters, dual lumen catheters, or multiple lumen catheters. Also, the presence of a particular tip geometry at the entrance to at least one lumen minimizes the catheter""s tendency to become suctioned against the vessel wall and ensures high flow rate.
In one aspect, the invention relates to a catheter comprising a hub and a generally elongated conduit having a substantially continuous and smooth wall. The conduit defines at least one lumen and has a length extending from a proximal end to a distal end of the conduit. The proximal end is coupled to the hub and the distal end has an opening in communication with the lumen. The conduit is conical and tapered along its length from the hub to the opening. The substantially continuous and smooth conduit wall has no openings, apertures, holes, roughness, or indentations over substantially all of its length.
Embodiments of this aspect of the invention can include the following features. For example, the wall can have a notch distal to the distal end, and the notch can communicate with at least one of the lumens. The notch can comprise a longitudinal cut in the conduit. The notch can include a distal appendage. The notch can comprise an opening having an area greater than that of a transverse cross-sectional area of the conduit immediately proximal to the opening. In dual lumen embodiments, a first lumen may extend from the proximal end to the opening at the distal end and a second lumen may extend from the proximal end to a point distally beyond the opening which may have a second opening. Also, the conduit may be conical and tapered from the proximal end to the point distally beyond the opening.
The conduit wall can have a thickness greater at the proximal end than at the distal end, and the thickness of the wall can transition between the proximal end and the distal end. At least one of the lumens can increase in cross-sectional area from the distal end to the proximal end or a portion thereof. A surface of the conduit can be treated, with heparin, for example, to inhibit association of materials, including biological materials, with the conduit (e.g., inhibit deposit of materials on the surface and/or inhibit materials from surrounding the conduit). The conduit can be generally conical, and the conduit can be a truncated cone in shape.
A transverse cross-section of the conduit can be round or oval, for example. A transverse cross-section of at least one of the lumens can be circular or partly circular, for example. At least a portion of the conduit can be curved. At least a portion of the conduit can be reinforced with, for example, a fiber, a wire, a material that is harder than the conduit, and/or a material that is softer than the conduit. The conduit can further comprise at least one cuff. The conduit also can further comprise at least one internal divider defining at least two lumens.
The catheter can further comprise at least one connecting tube connected to the hub. At least one of the connecting tubes can be in communication with at least one of the lumens. At least one of the connecting tubes can be curved and oriented in parallel with a distal portion of the conduit, straight and oriented approximately 180 degrees from a distal portion of the conduit, or oriented somewhere between these two positions. One or more of the connecting tubes can be selectively removable (e.g., so that it can be replaced if damaged).
At least one of the internal dividers can have a thickness greater at the proximal end than at the distal end, and the thickness can transition between the proximal end and the distal end. At least a portion of one of the internal dividers can be reinforced with a material stiffer than the conduit. One or more of the internal dividers can be connected with the wall of the conduit distal to the notch.
In another aspect, catheters according to the invention comprise a hub and a flexible, generally elongated conduit having an outer wall and defining at least one lumen. The conduit comprises a proximal section extending from a proximal end, which is coupled to the hub, to a first point. The proximal section has a first cross-sectional area along its length. A middle section extends from the first point to a second point. The first cross-sectional area at the first point is larger than a second cross-sectional area at the second point. A distal section extends from the second point to a distal end. The distal section has the second cross-sectional area along its length. The thickness of the wall increases in a distal to proximal direction over at least a portion of the conduit. At least one lumen has a cross-sectional area that increases in a distal to proximal direction over at least a portion of the conduit. In certain embodiments, the thickness of the wall increases in thickness from the second point to the first point and the cross-sectional area of at least one lumen increases from the second point to the first point.
In certain embodiments, a surface of the conduit can be treated, with heparin, for example, to inhibit association of materials, including biological materials, with the conduit (e.g., inhibit deposit of materials on the surface and/or inhibit materials from surrounding the conduit). The conduit can further comprise at least one cuff. The conduit also can further comprise at least one internal divider defining at least two lumens. At least one of the internal dividers can have a thickness greater at the proximal end than at the distal end, and the thickness can transition between the proximal end and the distal end. A first lumen may extend from the proximal end to the opening at the distal end and a second lumen may extend from the proximal end to a point distally beyond the opening which may have a second opening. At least a portion of the conduit can be reinforced with, for example, a fiber, a wire, a material that is harder than the conduit, and/or a material that is softer than the conduit. The catheter can further comprise at least one connecting tube connected to the hub. At least one of the connecting tubes can be in communication with at least one of the lumens.
Methods of positioning or placing catheters according to the invention, as well as methods of making the catheters by extrusion, are described and constitute aspects of the invention. One method involves placing a catheter of the type described above by inserting it into a vessel having a breach and then positioning it within the vessel. Another method involves making a catheter of the type described above by extruding it into the desired shape such as a conical shape.
The foregoing and other objects, aspects, features, and advantages of the invention will become more apparent from the following description and from the claims.